Light translating system



Ap 9 R'@ H. RANGER LIGHT TRANSLATING SYSTEM Filed June 30, 1931 g ll INVENTOR R. H. RANG BY A oRN Patented Apr. 14, 1936 UNITED STATES LIGHT TRANSLATING SYSTEM Richard Howland Ranger, Newark, N. J assignor to Radio Corporation of America, a corporation of Delaware Application June 30, 1931, Serial No. 547,865

12 Claims.

The present invention relates to light translating apparatus and particularly to light translating apparatus for use in the reproduction of record subjects whether said reproduction is accomplished by facsimile transmission, television, light-responsive photo engraving apparatus or any other suitable means.

In order to avoid many difficulties in connection with the amplification of the response from light sensitive translating elements due to the so-called D. C. amplifier systems, it has been found suitable to rely upon apparatus now known in the art as A. C. photo amplifiers. Accordingly, many and various schemes for introducing alternating currents into light translating elements or the like have been proposed. Most of the systems known in the art introduce into the cell a chopper frequency by Way of interruption of a light beam causing the response. However, such systems have the objection that only half of the available time period is used for translating the light values of the record, of which an image is to be reproduced, into suitable current values because of the fact that the light striking or impinging upon the light translating element mustbe alternately turned on and. off. The off period corresponds to substantially one-half the total time period available.

Other systems which do not have the objection of limiting the useful response period of the light translating element to one-half the total time available, introduce an alternating current of suitable frequency, such as a tone or carrier frequency, upon the photo cell either directly or by Way of a suitable Wheatstone bridge connection. However, such systems require for the manifestation additional apparatus. They complicate the general assembly and provide additional parts and instrumentalities with which difficulty may be encountered.

Therefore, the present invention has as one of its aims and objects that of so arranging the light translating system that the light values corresponding to the varying intensities of light and shadow of successive or even separated elemental sections of a record surface may be caused to influence at all times a light translating element, but nevertheless to so control the variable intensity light that each of a plurality of light translating elements are influenced alternately, each for substantially half the available transmission time. To avoid the objections of the systems of the prior art, above discussed, the useful output from the light translating elements is connected push-pull so that when there is an absence of output current from one light translating element there is an available output energy from the other light translating element, and vice versa, which may control a transmitter or under some conditions control directly a reproducing apparatus.

Further objects of the invention areto overcome the non-linear response difiiculties oi systems existing in the prior art and to so arrange the light translating system that the response 101 therefrom Will be substantially linear. It is well known that the output from any photo-electric tube, irrespective of the light color response, or from any other suitable light translating apparatus is not truly. linear. There is, however, a 15 portion of the output curve of practically all photo-tubes wherein output current is plotted against light intensity where the response in the output is close to a linear function. However, this photo-tube current-light intensity output current curve does not assume a linear function until the light translating element or photo-tube has been influenced by light of an intensity greater than a certain predetermined intensity, depending of course upon the particular tube characteristic. Therefore, in order to overcome these difficulties I have chosen to bias each light translating element by light of a constant intensity suficient to bring the response of the photo-tube or other light translating element to a point Where additional light which, in this instance, is the picture controlled light, will cause a resulting output which is substantially linear. Such a light has become known in the art as a C light and has been disclosed in connection with a D. C. photo amplifier by my United States Patent No. 1,738,315 granted to me on December 3, 1929.

The interruption of a light beam and the alternate projection thereof to each of a plurality of light translating elements has been set forth broadly by my copending application Serial No. 316,157, filed October 31, 1928, now Patent No. 1,811,895, granted June 30, 1931, and United States Patent No. 1,789,687 granted to me on January 20, 1931. However, in my aforesaid Patent No. 1,738,315 the system disclosed did not set forth an A. C. amplifier of photoelectric currents of a type which would produce a linear response. Therefore, as a primary object of my invention I have sought to develop a method and means by which a truly linear output may be obtained in a photo amplifying system for all light values on a record surface between minimum light, or

black, or maximum light, or white, on the photoelectric tube.

Another object of the invention is to provide a system which, in addition to producing a more linear output from the photocell amplifier system, tends to increase the overall efliciency of operation by raising the output of the photocell amplifier system above theusual noise level.

Further objects and advantages of my system are to provide, in a manner to be hereinafter set forth, convenient apparatus and means for accomplishing the result, it being understood that compactness of arrangement, efficiency of use, and convenience of installation are important considerations in the development of the invention.

Still further and other objects and advantages of the invention will become apparent and at once suggest themselves to those skilled in the art to which the invention relates by reading the following specification and claims in connection with the accompanying drawing, wherein:-

Fig. 1 illustrates conventionally an arrangement wherein linear response characteristics may be obtained from a plurality of light translating elements to represent each of a plurality of light paths on a record surface;

Fig. 2 illustrates a further portion of the optical system of Fig. 1;

Fig. 3 illustrates the connection of the photo tube amplifying system; and,

Fig. 4 diagrammatically represents the plate current-light intensity curve for each of the amplifiers connected with the photo tubes of Fig. 3.

Now referring to the drawing, light varying in intensity in accordance with the intensity of light and shadow on successive elemental areas of a record subject of which an image is to be reproduced is directed through a suitable optical system I I along a path I3 to a disc I5 or other suitable light directing apparatus. The disc I5 preferably comprises either a single track or a plurality of concentrically arranged tracks of apertures I'I between which are reflecting surfaces I9, as has been disclosed in my Patent No. 1,789,687. The disc I5 is rotated by any suitable driving means at a constant speed in the direction shown by the arrow, for example, about the shaft or spindle 2 I. As the disc rotates, light of varying intensity corresponding to the varying intensities of light and shadow on successive elemental areas of the recording surface is projected along the path I3, the light beams being either passed through an aperture I! or being reflected from the disc by one of the reflecting surfaces I9. Thus, as disc I5 is rotated, and assuming that the apertures and reflecting surfaces are each of equal width, light will first pass through the disc through an aperture and then be reflected from the disc after which the cycle of operation will be repeated. Due to the equal size or width of the apertures and the reflecting surface, the time period of direct transmittal of the varying intensity light ray or the reflection of the variable intensity light ray will be equal.

The light of variable intensity, representing the record for transmission, upon passing through the disc will travel along a path designated as 23 while the light reflected from the disc will travel along a path designated as 25, the first light path 23 then passing through a suitable optical system preferably in the form of a prism 21 from which it passes through a diaphragm (not shown) in the housing 29 which houses a photo tube such as is shown at 3| on Fig. 3. Light reflected from the disc along a path 25 passes through a similar diaphragm or slot 33 of the housing 35 so as to influence and produce a response from the photo tube element contained therein, which is similar to the photo tube element diagrammatically shown as 31 on Fig. 3.

Simultaneous to the influence of the photo tubes 3| and 3'! by the variable intensity, light ray I3 as directed along either path 23 to influence photo tube 3| or path 25 to influence the photo tube 31; light of a constant intensity, known as a C light, from a source (not shown) is directed by means of the optical system 39 along a path 4| so as to strike the disc element I5. The light path 4| is so arranged that as light is transmitted through the disc along path 23, the constant intensity light will be reflected from the disc along the path 43 and by means of the same optical element 21 used to direct the variable intensity light passing along path 23 to the photo tube 3 I, the constant intensity light passing along the path 43 is directed to the same photo tube. Upon a slight rotation of the disc I5 so as to cause the variable intensity light passing along path I3 to be reflected from the disc along path 25 by means of the reflecting surface I9 the constant intensity light from path 4| passes through an aperture IT in the disc I5 so as to be directed along a path 45 to influence photo tube element 3].

This simultaneous influence of the photo tubes 3| and 31 by means of the constant intensity light and the variable intensity light produces from the photo tubes an output current which is never less than the output produced from the constant intensity light or, in other words, a bias has been placed upon the photo tubes in a cyclical manner by the C light.

As the photo tubes 3| and 31 are alternately subjected to varying intensities of light and shadow, as well as constant intensities of light, responses are produced therefrom which produce varying potential drops in resistors 49 and 5| of Fig. 3. In accordance with the potential drop produced in either of resistors 49 or 5| by illumination of photo tubes 3| or 31 varying output currents will flow in the output circuit of the thermionic tubes 53 or 55 which are, as seen from Fig. 3, connected in push-pull. These currents flow in the primary windings 51 and 59 of transformer 6| so as to appear in the secondary 63 as pulsating currents of variable amplitude flowing at a frequency corresponding to the frequency at which the variable intensity light is interrupted in its effort to influence the photo tubes 3| or 37.

As is represented by Fig. 4 showing a diagram of plate current from tubes 53 and 55 plotted against the light intensity influencing the photo tubes 31 and 3| respectively, a liminal value of current is supplied by the C light influencing the photo tubes which liminal value is identified by the dash line indicated as C light. The current curve from tube 53 being designated as A and from tube 55 as B. Since these tubes have their outputs out of phase with respect to each other the identical output currents do not exist but are substantially as has been shown by the drawing. Consequently, net effective output from these tubes which appears in the secondary circuit 63 of transformer BI is the dotted line designated as E in Fig. 4.

Supposing, for example, that the disc I5 has only a single set of apertures arranged concentrically thereabouts. then as the disc rotates in the direction of the arrow the light beams varying in intensity and of constant intensity will be deflected from one to the other light translating elements at a frequency corresponding to the number of reflecting surfaces separating successive apertures of the disc times the number of revolutions per second that the disc makes. If multiplex transmission is resorted to so that there may be two or more simultaneously transmitted signals then the number of apertures on the disc for each concentric row of apertures will be different so that as the disc rotates a plurality of interruption frequencies proportionate to the number of apertures and reflecting surfaces in each path will cause responses from the photocells. These various tonal or carrier frequencies may then be separated at the receiving point by suitable apparatus as has been disclosed in my abovementioned copending applications.

While the present invention does not show specifically the exact type of light pick-up device which I propose to use, it nevertheless is to be understood that such pick-up device may be constructed and built in accordance with the teachings in my United States Patent No. 1,803,133 granted to me on April 28, 1931, wherein is disclosed a picture transmitting and reproducing apparatus termed a universal machine which is capable of transmitting and reproducing pictures at variable speeds and in variable detail depending, of course, upon the quality of reception desired and the quality of transmission which is obtainable at predetermined time periods. The illumination beams for illuminating the record which is to be transmitted, assuming, for example, that the translating apparatus hereindisclosed is to be applied to facsimile transmission or any other suitable systems for reproduction of transmission reception may be constructed in accordance with t e teachings in my copending application Serial No. 321,821, filed November 26, 1928.

While only one form of. my invention has been discussed in this specification, it is, of course, obvious that many and varied changes may be made therein without departing from the spirit and scope of the invention provided the fundamental principle herein taught remains, that being, of course, to generate in the light translating element itself a tonal or carrier frequency and then to cause varying changes of light intensities striking the light translating elements to produce output responses therefrom which are never below a predetermined definite output.

I therefore believe myself to be entitled to make any and all modifications of this invention which fall fairly within the spirit and scope thereof, and which would suggest themselves to those skilled in the art to which the invention relates.

Having now described my invention, what I claim and desire to secure by Letters Patent of. the United States is as follows:

1. In a light translating system a plurality of light translating elements, means for alternately subjecting each of said elements to light of constant intensity, and means for subjecting the illuminated light translating elements to light of variable intensity independently of said constant light, said variable light varying in proportion to variations in intensity of light and shadow on elemental areas of a record of which an image is to be reproduced during time periods corresponding to the constant illumination.

2. In a light translating system a plurality of light translating elements, means for alternately subjecting each of said elements to light of constant intensity, and means for simultaneously superimposing upon the said constant intensity light a second light of. variable intensity independently of said first light, said second light varying in proportion to variations in intensity of light and shadow on elemental areas of a record of which an image is to be reproduced.

3. In a light translating system a plurality of light translating elements, means for connecting the output from each of said elements push-pull, means for subjecting alternately each of said light translating elements to feeble intensity light of constant intensity for varying the initial point of response of said element to variable intensity light to a point from which changes in light will produce substantially linear outputs, and means for simultaneously subjecting each of said light translating elements to light of variable intensity as varied in intensity in accordance with variations in the light and shadow on elemental areas of a record subject of which an image is to be reproduced.

4. In a light translating system a plurality of light translating elements, means for connecting the output from each of said elements push-pull, means for subjecting alternately each of said light translating elements to light of constant intensity for maintaining the initial point of response of said element to increased intensity of light at a point from which increases in light intensity will produce substantially linear outputs, and means for simultaneously subjecting each of said light translating elements to light of variable intensity as varied in intensity in accordance with variations in the light and shadow on elemental areas of a record subject of which an image is to be reproduced.

5. In a light translating system for recording and reproducing apparatus, a light path of variable intensity varying in accordance with'varying intensities of light and shadow of elemental sections of a record of which an image is to be produced, a plurality of light translating elements connected with their output in push-pull, means for alternately projecting said variable intensity light beam upon each of said light trans lating elements for illuminating said elements each for substantially half of any unit time period whereby due to the interruption in the light on said elements a carrier frequency modulated in accordance with the varying intensity of light and shadow influencing said elements appears in the push-pull output, and means for illuminating each light translating element simultaneously with the variable intensity illumination with illumination of constant intensity for causing a linear response characteristic from said light translating system upon the application of variable intensity light thereto.

6. In a light translating system for recording reproducing apparatus, a light path of variable intensity varying in accordance with varying intensities of light and shadow of elemental sections of a record of which an image is to be produced, a plurality of light translating elements having their output connected push-pull fashion, means for alternately projecting and changing said variable intensity illumination from one to the other of said light translating elements for illuminating said elements each for substantially half of any unit time period whereby due to the interruption in the light on said elements a carrier frequency modulated in accordance with the varying intensity of light and shadow influencing said elements appears in the push-pull output, and a biasing light for illuminating each light translating element simultaneously with the variable intensity illumination thereof with light of substantially constant intensity for causing a linear response characteristic from said light translating system upon the application of Variable intensity light thereto.

7. In picture transmitting apparatus, a plurality of light translating elements, means for producing light of predetermined constant intensity, means for producing light of variable intensity to represent intelligence for transmission, and means for sequentially influencing the light translating elements each simultaneously With both the produced constant and variable light so that in the output circuits of the light translating elements signals of a frequency proportionate to the rate of illumination appear and so that the amplitude of the signals varies from a predetermined minimum value to a maximum value proportionate to the signal strength due to maximum brilliance of the variable light intensity.

8. In picture transmitting apparatus, a plurality of light translating elements, means for producing light of predetermined constant intensity, means for producing light of variable intensity to represent intelligence for transmission, and light chopping means for sequentially influencing the light'translating elements each simultaneously with both the produced constant and variable light so that in the output circuits of the light translating elements signals of a frequency proportionate to the rate of illumination appear and so that the amplitude of the signals varies from a predetermined minimum value to a maximum value proportionate to the signal strength due to maximum brilliance of the variable light intensity.

9. In picture transmitting apparatus, a plurality of photoelectric tubes having their output circuits connected in push-pull fashion, means for producing light of predetermined constant intensity, means for producing light of variable intensity to represent intelligence for transmission, and means for sequentially influencing the light translating elements each simultaneously with both the produced constant and variable light so that in the output circuits of the light translating elements signals of a frequency proportionate to the rate of illumination appear and so that the amplitude of the signals varies from a predetermined minimum value to a maximum value proportionate to the signal strength due to maximum brilliance of the variable light intensity.

10. In picture transmitting apparatus, a plurality of photoelectric tubes having their output circuits connected in push-pull fashion, means for producing light of predetermined constant intensity, means for producing light of variable intensity to represent intelligence for transmission, and light chopping means for sequentially influencing the light translating elements each simultaneously with both the produced constant and variable light so that in the output circuits of the light translating elements signals of a frequency proportionate to the rate of illumination appear and so that the amplitude of the signals varies from a predetermined minimum value to a maximum value proportionate to the signal strength due to maximum brilliance of the variable light intensity.

11. An alternating current generator system comprising a pair of photoelectric tubes having their output circuits connected push-pull fashion, means for producing constant intensity light, means for alternately influencing each of said photoelectric tubes by the constant intensity light so that in the push-pull output circuit of the photoelectric tubes an alternating current of a frequency proportionate to the rate of illumination of the photoelectric tubes by the constant light appears, and means for subjecting each photo tube to variable light intensity simultaneously with the constant light intensity so that the amplitude of the generated alternating current varies above the predetermined amplitude produced by the constant intensity light by amounts proportionate to the intensity of the impressed variable intensity light While maintaining the same frequency of the alternating current.

12. In combination a pair of light responsive elements having a common output circuit, means for sequentially subjecting the elements to the influence of variable intensity light to produce in the output circuit electrical energy of a frequency corresponding to the rate of illumination of the light responsive elements and of amplitude value varying between a maximum producible by maximum brilliance of illumination and a minimum producible by absence of illumination, and means for subjecting each light responsive element to light of constant intensity during the application of the variable light so as to control the minimum amplitude of the light modulated electrical energy appearing in the output circuit.

RICHARD HOWLAND RANGER. 

